HomeMy WebLinkAboutSubsoil Study for Foundation Design 08.28.2017,(æint/ t-z/-Øzz
H-PVKUMAR 5020 County Road 154
Glenwood Springs, CO 81601
Phone: (970) 945-7988
Fax (970) 945-8454
Email: hpkglenwood@kumarusa.com
Office Locations: Ðenver (HQ), Parker, Colorado Springs, Forl Collins, Glenwood Springs, Summit County, Colorado
STJBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 50, FILTNG 3,IRONBRTDGE
1817 RIVERBEND IVAY
GARFIELD COUNTY, COLORADO
PROJECT NO. 17-7-563
AUGUST 28,2017
PREPARED FOR:
KIRK CHENEY
2902 COANTY ROAD 113
CARßONDALE, CO 81623
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Geotechnical Engineering I Bgineering Geology
Malerials Testing I Environrrental
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY
PROPOSED CONSTRUCTION
STTE CONDITIONS
GEOLOGY
FIELD EXPLORATION ........
SUBSURFACE CONDITIONS ..
FOUNDATION BEARING CONDITIONS
DES IGN RECOMMENDATIONS
FOUNDATIONS
FLOOR SLABS
UNDERDRAIN SYSTEM ........
SURFACE DRAINAGE
LMTTATIONS..
FIGURE 1 . LOCATION OF EXPLORATORY BORING
FIGURE 2 -LOG OF EXPLORATORY BORING
FIGURE 3 - S}VELL-CONSOLIDATION TEST RESULTS
FIGURE 4 - GRADATION TEST RESULTS
TABLE I- SUMMARY OF LABORATORY TEST RESULTS
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H-P\KUMAR
Project No.1 7-7-563
PURPOSE AND SCOPE OF STUDY
This report presents the results ofa subsoil study for a proposed residence to be located on Lot
50, Filing 3, Ironbridge, 1817 River Bend Way, Garfield County, Colorado. The project site is
shown on Figure 1. The purpose of the study was to develop recommendations for the
foundation design. The study was conducted in accordance with our agreement for geotechnical
engineering services to Kirk Cheney dated July 17,2017.
An exploratory boring was drilled to obtain information on the subsurface conditions. Samples
of the subsoils obtained during the field exploration were tested in the laboratory to determine
their classification, compressibility or swell and other engineering characteristics. The results of
the field exploration and laboratory testing were analyzed to develop reconmendations for
foundation types, depths and allowable presswes for the proposed building foundation. This
report summarizes the data obtained durring this study and presents our conclusions, design
recommendations and other geotechnical engineering considerations based on the proposed
construction and the subsurface conditions encountered.
PROPOSED CONSTRUCTION
Development plans were concsptual at the time of our study. In general, the proposed residence
will be a2,4AA square foot structure with an attached 3 car garage. Ground floor will be
structural over a crawlspace. The garage floor will be slab-on-grade. Grading for the structure is
assumed to be relatively minor with cut depths between about 2to 4 feef. We assume relatively
light foundation loadings, typical of the proposed type of construction.
If building loadings, location or grading plans change significantly from those described above,
we should be notified to re-evaluate the recommendations contained in this report.
SITE CONDITIONS
The site was vacant at the time of our field work. The lot slopes gently down to the north.
Vegetation consists of sparse weeds. There is shallow fill on the site from grading performed
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during the subdivision development. The Roaring Fork River is located downhill about 7¿ mile
to the north.
GEOLOGY
The geologic conditions were described in a previous report conducted for planning and
preliminary design of the overall subdivision development by Hepworth-Pawlak Geotechnical
(now HP/Kumar) dated October 29,1997, Job No. L97 327. The surficial soils on the lot mainly
consist of sandy silt and clay alluvial fan deposits with interbedded sandy and gravelly layers
overlying gravel terrace alluvium of the Roaring Fork River. The river alluvium is mainly a
clast-supported deposit ofrounded gravel, cobbles and boulders typically up to about 2to3 feet
in size in a silty sand matrix and overlies siltstone/claystone bedrock.
Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Ironbridge subdivision.
These rocks are a seqllence of gypsiferous shale, fine-grained sandstone and siltstone with some
massive beds of gypsum and limestone. Dissolution of the gypsum under certain conditions can
cause sinkholes to develop and can produce areas oflocalized subsidence. A sinkhole occurred
in the parking lot adjoining the golf cart storage tent in January, 2005 located about % mlle to the
southeast of Lot 50 which was backfilled and compaction grouted. To our knowledge, that
sinkhole has not shown signs of reactivation such as ground subsidence since the remediation.
Sinkholes possibly related to the Evaporite were not observed in the immediate area of the
subject lot. Based on our present knowledge of the subsurface conditions at the site, it cannot be
said for certain that sinkholes related to the underlying Evaporite will not develop. The risk of
future ground subsidence on Lot 50 throughout the service life of the proposed building, in our
opinion, is low; however, the owner should be made aware of the potential for sinkhole
development. If further investigation of possible cavities in the bedrock below the site is desired,
we should be contacted.
FIELD EXPLORATION
The field exploration for the project was conducted on luly 24,2017 . One exploratory boring
was drilled at the location shown on Figure 1 to evaluate the subsurface conditions. The boring
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was advanced with 4 inch diameter continuous flight augers powered by a truck-mounted CME-
458 drill rig. The boring was logged by a representative of H-PlKumar.
Samples of the subsoils were taken with l% inch and 2 inch LD. spoon samplers. The samplers
were driven into the subsoils at various depths with blows from a 140 pound hammer falling 30
inches. This test is similar to the standard penetration test described by ASTM Method D-1586.
The penetration resistance values are an indication of the relative density or consistency of the
subsoils. Depths at which the samples were taken and the penetration resistance values are
shown on the Log of Exploratory Boring, Figure 2. The samples were returned to our laboratory
for review by the project engineer and testing.
SUBSURFACE CONDITIONS
A graphic log of the subsurface conditions encountered at the site is shown on Figure 2. The
subsoils consist of about lVz feet of very stiff clay and gravel fill overlyin g 6Yz feet of stiff sandy
silty and clay. Dense, slightly silty sandy gravel with cobbles was encountered below the clay at
a depth of 8 feet down to the bottom of the boring, 15 feet. Drilling in the dense granular soils
with auger equipment was difficult due to the cobbles and possible boulders.
Laboratory testing performed on samples obtained f¡om the boring included nafural moisture
content, density and gradation analyses. Results of swell-consolidation testing performed on
relatively undisturbed drive samples of the clay soils, presented on Figure 3, indicate low
compressibility under light loading and a low expansion potential when wetted under light
loading. Results of gradation analyses performed on a small diame¡er drive sample (minus 172
inch fraction) of the coarse granular subsoils are shown on Figure 4. The laboratory testing is
summarized in Table 1.
No free water was encountered in fhe boring at the time of drilling the subsoils were slightly
moist
FOUNDATION BEARING CONDITIONS
Spread footing foundations placed on the clay subsoils should be adequate for support ofthe
proposed residence. Although the clay soil samples showed a low expansion potential when
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tested, our experience in this area is that expansion shown in the tests is not indicative of the
typical behavior of the clays soils in this area. The expansion potential should be further
evaluated at the time of excavation.
DESIGN RECOMMENDATIONS
FOTINDATIONS
Considering the subsurface conditions encountered in the exploratory boring and the nature of
the proposed construction, we recommend the building be founded with spread footings bearing
on the natural clay soils.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural soils should be designed for an
allowable bearing pressure of_Lsmgl Based on experience, we expect
movement of footings designed and constructed as discussed in this section will
be about 1 inch or less.
2) The footings should have a minimum width of 18 inches for continuous walls and
2 feet for isolated pads.
3)Exte¡ior footings and footings beneath unheated areas should be provided with
adequate soil cover above their bearing elevation for frost protection. Placement
of foundations at least 36 inches below exterior grade is typically used in this
area.
4)Continuous foundation walls should be heavily reinforced top and bottom to span
local anomalies such as by assuming an unsupported length of at least 12 feet.
Foundation walls acting as retaining structures should also be designed to resist a
lateral earth pressure corresponding to an equivalent fluid unit weight of at least
55 pcf fo¡ the onsite soils as backfill.
All existing fill, topsoil and any loose or disturbed soils should be removed and
the footing bearing level extended down to the stiff natural clay soils. The
exposed soils in footing area should then be moistened and compacted.
5)
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A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
FLOOR SLABS
The natural on-site soils, exclusive of fill and topsoil, are suitable to support lightly loaded slab-
on-grade construction. To reduce the effects of some differential movement, floor slabs should
be separated from all bearing walls and columns with expansion joints which allow unrestrained
vertical movement. Floor slab control joints should be used to reduce damage due to shrinkage
cracking. The requirements for joint spacing and slab reinforcement should be established by the
designer based on experience and the intended slab use. A minimum 4 inch layer of road base
gravel should be placed beneath garage level slabs. This material should consist of minus 2 inch
aggrcgate with at least 5O7o retained on the No. 4 sieve and less than l27o passing the No. 200
sieve.
All fill materials for support of floor slabs should be compacted to at leasf 95Vo of maximum
standard Proctor density at a moisture content near optimum. Required fill should consist of
imported granular soils such as %-inch road base devoid of vegetation, topsoil and oversized
rock.
UNDERDRAIN SYSTEM
The proposed shallow (less than 4 feet) crawlspace and slab-on-grade garage should not require a
perimeter underdrain system provided that the site grading recommendations contained in this
report are followed. We recommend that below-grade construction, such as retaining walls, deep
crawlspace and basement areas, be protected from wetting and hydrostatic pressure buildup by
an underdrain system.
If installed, the drains should consist of drainpipe placed in the bottom of the wall backfill
surrounded above the invert level with free-draining granular material. The drain should be
placed at each level ofexcavation and at least I foot below lowest adjacent finish grade and
6)
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sloped at a minimum IVo to a suitable gravity outlet or drywell. Free-draining granular material
used in the underdrain system should contain less than ZVo passingthe No. 200 sieve, less than
507o passing the No. 4 sieve and have a maximum size of 2 inches. The drain gravel backfill
should be at least lVz feet deep. An impervious membrane such as 30 mil PVC should be placed
beneath the drain gravel in a trough shape and attached to the foundation wall with mastic to
prevent wetting of the bearing soils.
SURFACE DRAINAGE
Proper surface grading and drainage will be critical to prevent wetting of the bearing soils and
satisfactory performance of the foundation. The following drainage precautions should be
observed during construction and maintained at all times after the residence has been completed:
1) Inundation ofthe foundation excavations and underslab areas should be avoided
during construction.
2) Exterior backfill should be adjusted to near optimum moisture and compacted to
at least 95Vo af the maximum standard Proctor density in pavement and slab areas
and to at least 9AVo of the maximurn standard Proctor density in landscape areas.
3) The ground surface surrounding the exterior of the building should be sloped to
drain away from the foundation in all directions. We recommend a minimum
slope of 12 inches in the first l0 feet in unpaved areas and a minimum slope of 3
inches in the first l0 feet in paved areas. Free-draining wall backfill (if any)
should be capped with about 2 feet of the on-site soils to reduce surface water
infiltration. Graded swales should have a minimum slape of 3Vo.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
5) Landscaping which requires regular heavy iruigation should be located at least l0
feet from foundation walls. Consideration shor"rld be given to use of xeriscape to
reduce the potential for wetting of soils below the building caused by irrigation.
LIMITATIONS
This study has been conducted in accordance with generally accepted geotechnical engineering
principles and practices in this area at this time. We make no warranty either express or implied.
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Project No.17-7-563
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The conclusions and recommendations submitted in this report are based upon the dala obtained
from the exploratory boring drilled at the location indicated on Figure 1, the proposed type of
construction and our experience in the area. Our services do not include determining the
presence, prevention or possibility of mold or other biological contaminants (MOBC) deveioping
in the future. If the client is concerned about MOBC, then a professional in this special field of
practice should be consulted. Our findings include interpolation and extrapolation of the
subsurface conditions identified at the exploratory boring and variations in the subsurface
conditions may not become evident until excavation is performed. If conditions encountered
during construction appear different from those described in this report, we should be notified so
that re-evaluation of the recommendations may be made.
This report has been prepared for the exclusive use by our client for design purposes. We are not
responsible for technical interpretations by others of our information. As the project evolvcs, wc
should provide continued consultation and field services during construction to review and
monitor the implementation of our recommendations, and to verify that the recommendations
have been appropriately interpreted. Significant design changes may require additional analysis
o¡ modifications to the recommendations presented herein. We recommend on-site observation
ofexcavations and foundation bearing strata and testing ofstructural fill by a representative of
the geotechnical engineer.
Respectfully Submitted,
H-P* KUMAR
E. Hardin,
Reviewed by:
Steven L. Pawlak. P.E.
DEH/kac
H.P*KUMAR
Project No.'17-7-563
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APPROXIMATE SCALE-FEËT
17 -7 -563 H-PryKU]VIAR LOCATION OF EXPLORATORY BORING Fig. 1
BORING 1 LEGEND
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15 NOTES
THE TXPLORATORY BORING WÄS DRILTTD ON JULY 21, 2017
W H A 4-INCH DIAMETER CONTINUOUS FUGHI POWER AUGER.
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2. THT LOCAIIO¡I OF THI TXPLORATORY SORING WÂS MTASUREO
APPROX¡MATELY 8Y PÂCINç FROM FÊATURES SHOWN ON THE
SIIE PLAN PROVIDED.
3. THI TLTVATION OT THI TXPLORATORY BORING WAS NOT
MTÁSUREÐ ANO THE LOG OF THE EXPLORATORY BORING IS
PLONTD TO OEPTH,
4. THT EXPLORATORY BORINO LOCATION SHOULO 8E CONSIOERTD
ACCURÀÏT ONLY TO THE OIGRTT IMPIITD BY THT METHOI)
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5. THE LINES SEIY'EIN MATTRIALS SHOWN ON THE EXPLORATORY
BORING LOG REPRESENT THE ÂPPROXIMATE BOUNOARIES
EETWTTN MÂTERIAL TYPES ANO THE TRANSITIONS MAY 8E
GRAOUAL.
6. GROUNDWATER WAS NOI ENCOUNTTREO IN THT SORING AT THE
TIMT OF ORILLING.
7, LÂSORATORY TEST RESULTS:. WC = WÀIER CONTTNT (X) (AsTM D 2216);
ÐÐ = ORY DINSIIY (pcf) (ASïM 0 2216);
+4 = PERCENTÁGT RTTAINTI} ON NO. 4 SIEVE (ÄSTM O 122);
-2O(} = PTRCT|TAGE PASSING NO. 2OO SIEVE (ASTM O ItlO).
1 7-7-553 H-PVKUMAR LOG OF EXPLORATORY BORING Fig. 2
SÂMPLE OF: Sondy Silty Cloy
FROM:8oríng1@2.5'
WC = 6.2 %, DÐ = 109 pcf
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
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EXPANSION UNDER CONSTANT
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17 -7 *563 H.PVKUMAR SWELL_CONSOLIDATION TESÍ RISULTS Fig. 3
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1 7-7-563 H.PryKUMAR GRADATION TEST RESULTS Fig. 4
H.P*KUMARÏABLE 1SUMMARY OF LABORATORY TEST RESULTSProject No. 17-7-563GRAVÊL(%)SAND(/"1SILTV"lCLAY(1"1SOIL TYPËSandy silty claySlightly sandy siltyclaySlightly sandy siltyGRAVEL('/")SAND(Y")PERCENTPASSINGNO.200SIEVE899JJ10958NATURALDRYDENSITY(pcr)109NATURALMOISTUFECONTENT('/'',6.26.3BORINGDEPTH(ft)I2V2510